A dispute between French and U.S. discoverers of the RMS Titanic surfaced late yesterday in U.S. District Court as the expedition's American leader prepared to meet the press today for the first major public briefing on the discovery of the historic shipwreck.

The lawsuit, filed by lawyers for the French Institute for Research and Exploitation of the Sea (Infremer), sought to block any public distribution of pictures of the wreck without Infremer's consent at a news conference scheduled for 10:30 a.m. at the National Geographic Society.

Lawyers for Infremer said the institute claimed a copyright interest in the 20,000-odd frames shot of the sunken liner, and said none of the pictures -- potentially worth millions of dollars -- should be released without its consent.

Judge Gerhard A. Gesell rejected the request for a temporary restraining order, ruling that the lawyers for the French institute had not proven their case.

That the suit was filed at all, however, threatens a major embarrassment for Robert Ballard of the Woods Hole Oceanographic Institution in Massachusetts, who only Monday returned home in triumph from the joint U.S.-French expedition praising his French colleagues for selfless cooperation.

Ballard is scheduled to be the major speaker at the press conference today. Infremer has scheduled a simultaneous press conference in Paris featuring Jean-Louis Michel, chief scientist aboard the French vessel Le Suroit.

The U.S. Navy research vessel Knorr, chartered by Woods Hole, discovered the Titanic last week some 500 miles off Newfoundland and 2 1/2 miles beneath the sea, using an underwater sonar and video system called ARGO developed by Woods Hole under a Navy contract. Earlier in the summer Le Suroit had covered 80 percent of the planned search area, using a sonar system developed by Infremer.

Yesterday Warren E. Dennis, a lawyer for Infremer, said Ballard had signed an agreement with Infremer giving the French institute a copyright interest in all photographs produced by the expedition. He said the French institute, which is privately funded, had already made distribution agreements for the photographs, films, and videotapes with television companies, magazines and other news organizations, though he declined to identify them.

But Dennis said he was told yesterday by lawyers for Woods Hole and the U.S. Navy that they considered the photographs to be in the public domain and not subject to a copyright interest by Infremer.

He said the photos were being kept in a vault in the Pentagon in the custody of the U.S. Navy.

Assistant U.S. Attorney Royce C. Lamberth, who represented the U.S. government at the hearing, confirmed that the photos were in the Navy's custody, though he said some of them may be at the National Geographic, which was processing the film.

Lamberth said the Woods Hole lab chartered the Knorr, using funds from another government agency, the National Science Foundation, which originally came from the Navy itself. "In effect," Lamberth said, "this is a Navy operation by a government contractor of the Navy." He said the government would not agree to any restrictions on the use of film, though he said he was uncertain how many pictures would be released today.

Dennis said it was unclear whether Infremer had a contract with Woods Hole or just with Ballard himself. He said his law firm in Washington had only received the first few pages of the 20-page agreement by telex from Paris.

"We don't have a clear understanding," Dennis said. But if many photos are released, he said, the value of first publication rights "evaporates instantly."

Michel and other French scientists were aboard the Knorr when the Titanic was discovered Sept. 1, 73 years after the ship struck an iceberg and sank. When the Knorr returned to Woods Hole on Tuesday, the French left immediately and flew to Paris.

Neither Ballard nor other Woods Hole representatives could be reached for comment last night.